We suspect DS1 may have HFA/Aspergers & are going to look at a pre-school for him tomorrow. I'm torn about whether to mention our concerns straight away or to let them get to know him a bit first & then compare notes. My main reason for sending him in the first place is because I'm struggling with his behaviour & would like an objective opinion from someone who knows him, is trained to spot things & isn't his mother! 
I've always thought completely open & honest information sharing is important but on the other hand I'm wondering if it wouldn't be better just to let them get to know him just as him before I push for more observations. He's very good at masking it - unless he suddenly bolts I'm not sure many people would notice much when they first meet him. I've discovered that once he gets comfortable with the new environment he starts displaying more of the behaviour we've seen at home. I don't want them to see me initially as an overly concerned parent if I was I might have been perturbed by his passive first year, instead of thrilled at having an 'easy' baby & dismiss my concerns in the first week because he seems 'normal'.
I should say, I have a level 5 in early childhood development, much of which focussed on things like ASD, my niece has ASD, we strongly suspect BIL & FIL both have HFA & the list of traits in women reads like me on paper. I'm well aware of the subtle indications of ASD that those who don't know about it might dismiss as being a boy/toddler. I'm virtually certain that he's on the spectrum but do have wobbles that I'm overly sensitive to the potential signs & seeing things that aren't there because of my training!
Sorry, rambling... Do I tell the pre-school from the off or take a more relaxed approach & raise it when he's been there a term or so? We're planning on HE eventually so ideally I'd like to get the ball rolling while he's at pre-school so I don't want to leave it too long before mentioning it!